The invention relates to a display device comprising an electro-optical medium between two supporting plates provided with electrodes which define pixels at overlap locations. The invention particularly relates to such a display device in which the electrodes on at least one supporting plate extend on the supporting plate beyond the area of the pixels where they are provided with drive elements.
The electro-optical medium is, for example a liquid crystal material, particularly a (super)twisted nematic liquid crystal material.
Such display devices are used in alphanumerical displays for measuring instruments, dashboards etc., but also, for example in computer monitor screens.
Display devices of the type described above are generally known. A problem which may occur particularly, but not exclusively in supertwisted nematic liquid crystal display devices is the phenomenon of discoloration because the distance between the two supporting plates is not the same throughout; notably this distance differs at the location of (between) two pixel-defining electrodes from that at the location of (between) an electrode and a supporting plate not provided with an electrode. Since the color difference increases at larger thicknesses of the electrodes, this problem frequently occurs in display devices in which the electrodes on at least one supporting plate extend on the supporting plate beyond the area of the pixels where they are provided with drive elements, because the electrode tracks should have a minimum thickness to ensure a good contact for connecting these drive elements, for example via chip-on-glass (COG) techniques. Moreover, a certain thickness is advantageous because there will be less voltage drop across the electrode and a more uniform display is obtained. The minimum thickness for this purpose is approximately 100 nm.